Brain's Protective Barrier Disintegrates as People Age: Accelerated Deterioration of Blood-Brain Wall May Play Role in Memory Loss, Learning Problems

Article excerpt

Time can wear down the sturdiest walls, even the one that protects the brain from bad stuff in the blood. This blood-brain barrier breaks down with age, possibly playing a role in Alzheimer's disease, a new study suggests.

Images in the Jan. 21 Neuron show direct evidence that aging influences the breakdown of the blood-brain barrier and that accelerated deterioration could contribute to learning and memory problems later in life.

Researchers in California detected the deterioration in high-resolution MRI scans of the brains of living people. Younger brains weren't as leaky as older brains, specifically in regions crucial for learning and memory. The images also revealed that older people with slight memory and learning difficulties had substantially more blood-brain barrier deterioration than healthy people of similar ages.

"This is a major advance," says neuroscientist Costantino Iadecola of Weill Cornell Medical College in New York City. Previous studies had suggested that the breakdown in the blood-brain barrier was linked to aging and memory problems, but that connection had not been shown in the brains of living people. "Now it has, and we have to put this thing back up on the board as a factor contributing to dementia," Iadecola says.

The blood-brain barrier is made up of sets of cells that zip tightly together around blood vessels in the brain. This firmly sealed layer creates a nearly impenetrable fortress that keeps potential toxins in the blood out of the brain. Tracking whether certain compounds breach the seal offers clues to the barrier's leakiness.

A group led by neuroscientist Berislav Zlokovic of the University of Southern California in Los Angeles tracked the chemical element gadolinium in MRI brain scans. Imaging the brains of healthy people ages 23 to 91 showed that the blood-brain barrier's leakiness begins in the hippocampus, a region crucial for learning and memory, and was greater in older brains. In people ages 55 to 85 who had mild learning and memory difficulties, the disintegration of one region in the hippocampus was 53 percent greater than in healthy people of similar ages.

"Focusing on the damage of the blood-brain barrier shows that it is an important factor possibly initiating changes in the brain that lead to dementia," Zlokovic says.

His team's images also showed that the breakdown of the barrier was linked to damage to pericyte cells, which are part of the blood-brain wall. …